| RFC 9275 | ALTO-PV | September 2022 |
| Gao, et al. | Experimental | [Page] |
This document is an extension to the base Application-Layer Traffic Optimization(ALTO) protocol. It extends the ALTO cost map and ALTO property map services sothat an application can decide to which endpoint(s) to connect based not only onnumerical/ordinal cost values but also on fine-grained abstract information regarding thepaths. This is useful for applications whose performance is impacted byspecific components of a network on the end-to-end paths, e.g., they may inferthat several paths share common links and prevent traffic bottlenecks byavoiding such paths. This extension introduces a new abstraction called the "AbstractNetwork Element" (ANE) to represent these components and encodes a network pathas a vector of ANEs. Thus, it provides a more complete but still abstract graphrepresentation of the underlying network(s) for informed traffic optimizationamong endpoints.¶
This document is not an Internet Standards Track specification; it is published for examination, experimental implementation, and evaluation.¶
This document defines an Experimental Protocol for the Internet community. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are candidates for any level of Internet Standard; see Section 2 of RFC 7841.¶
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained athttps://www.rfc-editor.org/info/rfc9275.¶
Copyright (c) 2022 IETF Trust and the persons identified as the document authors. All rights reserved.¶
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶
Network performance metrics are crucial for assessing the Quality of Experience(QoE) of applications. The Application-Layer Traffic Optimization (ALTO) protocol allows Internet Service Providers(ISPs) to provide guidance, such as topological distances between different endhosts, to overlay applications. Thus, the overlay applications can potentiallyimprove the perceived QoE by better orchestrating their traffic to utilize theresources in the underlying network infrastructure.¶
The existing ALTOcost map (Section 11.2.3 of [RFC7285]) and Endpoint Cost Service (Section 11.5 of [RFC7285]) provide only cost information for an end-to-end path defined byits <source, destination> endpoints: the base protocol[RFC7285] allows theservices to expose the topological distances of end-to-end paths, while variousextensions have been proposed to extend the capability of these services, e.g.,to express other performance metrics[ALTO-PERF-METRICS], toquery multiple costs simultaneously[RFC8189], and to obtain time-varyingvalues[RFC8896].¶
While numerical/ordinal cost values for end-to-end paths provided bythe existing extensions are sufficient to optimize the QoE of manyoverlay applications, the QoE of some overlay applications alsodepends on the properties of particular components on the paths. For example, job completion time, which is animportant QoE metric for a large-scale data analytics application, is impactedby shared bottleneck links inside the carrier network, as link capacity mayimpact the rate of data input/output to the job. We refer to such components ofa network as Abstract Network Elements (ANEs).¶
Predicting such information can be very complex without the help of ISPs; forexample,[BOXOPT] has shown that finding the optimal bandwidth reservation formultiple flows can be NP-hard without further information than whether areservation succeeds. With proper guidance from the ISP, an overlay applicationmay be able to schedule its traffic for better QoE. In the meantime, it may behelpful as well for ISPs if applications could avoid using bottlenecks orchallenging the network with poorly scheduled traffic.¶
Despite the claimed benefits, ISPs are not likely to expose raw details on their network paths: first because ISPs have requirements to hide their network topologies, second because these details may increase volume and computation overhead, and last because applications do not necessarily need all the network path details and are likely not able to understand them.¶
Therefore, it is beneficial for both ISPs and applications if an ALTO serverprovides ALTO clients with an "abstract network state" that provides thenecessary information to applications, while hiding network complexity andconfidential information. An "abstract network state" is a selected set ofabstract representations of ANEs traversed by the pathsbetween <source, destination> pairs combined with properties of these ANEs that are relevant to the overlay applications' QoE. Both anapplication via its ALTO client and the ISP via the ALTO server can achievebetter confidentiality and resource utilization by appropriately abstractingrelevant ANEs. Server scalability can also be improved bycombining ANEs and their properties in a single response.¶
This document extends the ALTO base protocol[RFC7285] to allow an ALTO server to convey "abstractnetwork state" for paths defined by their <source, destination> pairs. To thisend, it introduces a new cost type called a "Path Vector", following the costmetric registration specified in[RFC7285] and the updated cost moderegistration specified in[RFC9274]. A Path Vector is an arrayof identifiers that identifies an ANE, which can beassociated with various properties. The associations between ANEs and theirproperties are encoded in an ALTO information resource called the "entity propertymap", which is specified in[RFC9240].¶
For better confidentiality, this document aims to minimize information exposureof an ALTO server when providing Path Vector services. In particular, thisdocument enables the capability, and also recommends that 1) ANEs be constructed on demand and2) an ANE only be associated with properties that are requested by an ALTOclient. A Path Vector response involves two ALTO maps: the cost map, whichcontains the Path Vector results; and the up-to-date entity property map, whichcontains the properties requested for these ANEs. To enforce consistency andimprove server scalability, this document uses the "multipart/related" contenttype as defined in[RFC2387] to return the two maps in a single response.¶
As a single ISP may not have knowledge of the full Internet paths betweenarbitrary endpoints, this document is mainly applicable when¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14[RFC2119][RFC8174] when, and only when, they appear in all capitals, as shown here.¶
This document extends the ALTO base protocol[RFC7285] and the entityproperty map extension[RFC9240]. In addition tothe terms defined in those documents, this document also uses the followingterms:¶
An abstract representation for a component in a network that handles datapackets and whose properties can potentially have an impact on the end-to-endperformance of traffic. An ANE can be a physical device such as a router, alink, or an interface; or an aggregation of devices such as a subnetwork or adata center.¶
The definition of an ANE is similar to that for a network elementas defined in[RFC2216] in the sense that they both provide an abstractrepresentation of specific components of a network. However, they havedifferent criteria on how these particular components are selected.Specifically, a network element requires the components to be capable ofexercising QoS control, while an ANE only requires thecomponents to have an impact on end-to-end performance.¶
A string that uniquely identifies an ANE in a specific scope. An ANEcan be constructed either statically in advance or on demand based on therequested information. Thus, different ANEs may only be valid within aparticular scope, either ephemeral or persistent. Within each scope, an ANE isuniquely identified by an ANE name, as defined inSection 6.1. Note thatan ALTO client must not assume ANEs in different scopes but with the same ANEname refer to the same component(s) of the network.¶
Refers to a JSON array of ANE names. It is ageneralization of a BGP path vector. While a standard BGP path vector (Section 5.1.2 of [RFC4271]) specifies a sequence of Autonomous Systems (ASes) for adestination IP prefix, the Path Vector defined in this extension specifies asequence of ANEs for either 1) a source PID and adestination PID, as in the CostMapData object (Section 11.2.3.6 of [RFC7285]) or 2) asource endpoint and a destination endpoint, as in the EndpointCostMapDataobject (Section 11.5.1.6 of [RFC7285]).¶
An ALTO information resource (Section 8.1 of [RFC7285]) that supports theextension defined in this document.¶
A special cost type, which is specified inSection 6.5. When this costtype is present in an Information Resource Directory (IRD) entry, it indicates that the information resource isa Path Vector resource. When this cost type is present in a filtered cost maprequest or an Endpoint Cost Service request, it indicates that each cost value mustbe interpreted as a Path Vector.¶
The POST message sent to an ALTO Path Vector resource.¶
Refers to the multipart/related message returned by aPath Vector resource.¶
This section gives an illustrative example of how an overlay application canbenefit from the extension defined in this document.¶
Assume that an application has control over a set of flows, which may go throughshared links/nodes and share bottlenecks. The application seeks to schedule thetraffic among multiple flows to get better performance. The constraints offeasible rate allocations of those flows will benefit the scheduling. However,cost maps as defined in[RFC7285] cannot reveal such information.¶
Specifically, consider the example network shown inFigure 1. The network has sevenswitches ("sw1" to "sw7") forming a dumbbell topology. Switches "sw1", "sw2", "sw3",and "sw4" are access switches, and "sw5-sw7" form the backbone. End hosts "eh1" to"eh4" are connected to access switches "sw1" to "sw4", respectively. Assume that thebandwidth of link "eh1 -> sw1" and link "sw1 -> sw5" is 150 Mbps and the bandwidthof the other links is 100 Mbps.¶
+-----+ | | --+ sw6 +-- / | | \ PID1 +-----+ / +-----+ \ +-----+ PID2 eh1__| |_ / \ ____| |__eh2192.0.2.2 | sw1 | \ +--|--+ +--|--+ / | sw2 | 192.0.2.3 +-----+ \ | | | |/ +-----+ \_| sw5 +---------+ sw7 | PID3 +-----+ / | | | |\ +-----+ PID4 eh3__| |__/ +-----+ +-----+ \____| |__eh4192.0.2.4 | sw3 | | sw4 | 192.0.2.5 +-----+ +-----+bw(eh1--sw1) = bw(sw1--sw5) = 150 Mbpsbw(eh2--sw2) = bw(eh3--sw3) = bw(eh4--sw4) = 100 Mbpsbw(sw1--sw5) = bw(sw3--sw5) = bw(sw2--sw7) = bw(sw4--sw7) = 100 Mbpsbw(sw5--sw6) = bw(sw5--sw7) = bw(sw6--sw7) = 100 Mbps
The base ALTO topology abstraction of the network is shown inFigure 2.Assume that the cost map returns a hypothetical cost type representing the available bandwidth between a source and a destination.¶
+----------------------+ {eh1} | | {eh2} PID1 | | PID2 +------+ +------+ | | | | {eh3} | | {eh4} PID3 | | PID4 +------+ +------+ | | +----------------------+Now, assume that the application wants to maximize the total rate of the traffic amonga set of <source, destination> pairs -- say, "eh1 -> eh2" and "eh1 -> eh4". Let "x"denote the transmission rate of "eh1 -> eh2" and "y" denote the rate of "eh1 ->eh4". The objective function is¶
max(x + y).¶
With the ALTO cost map, the costs between PID1 and PID2 and between PID1 and PID4 willboth be 100 Mbps. The client can get a capacity region of¶
x <= 100 Mbps y <= 100 Mbps.¶
With this information, the client may mistakenly think it can achieve a maximumtotal rate of 200 Mbps. However, this rate is infeasible, as there are only twopotential cases:¶
"eh1 -> eh2" and "eh1 -> eh4" take different path segments from "sw5" to "sw7". Forexample, if "eh1 -> eh2" uses path "eh1 -> sw1 -> sw5 -> sw6 -> sw7 -> sw2 -> eh2"and "eh1 -> eh4" uses path "eh1 -> sw1 -> sw5 -> sw7 -> sw4 -> eh4", then the sharedbottleneck links are "eh1 -> sw1" and "sw1 -> sw5". In this case, the capacityregion is:¶
x <= 100 Mbps y <= 100 Mbps x + y <= 150 Mbps¶
and the real optimal total rate is 150 Mbps.¶
"eh1 -> eh2" and "eh1 -> eh4" take the same path segment from "sw5" to "sw7".For example, if "eh1 -> eh2" uses path "eh1 -> sw1 -> sw5 -> sw7 -> sw2 -> eh2"and "eh1 -> eh4" also uses path "eh1 -> sw1 -> sw5 -> sw7 -> sw4 -> eh4", then theshared bottleneck link is "sw5 -> sw7". In this case, the capacity region is:¶
x <= 100 Mbps y <= 100 Mbps x + y <= 100 Mbps¶
and the real optimal total rate is 100 Mbps.¶
Clearly, with more accurate and fine-grained information, the application canbetter predict its traffic and may orchestrate its resourcesaccordingly. However, to provide such information, the network needs to exposeabstract information beyond the simple cost map abstraction. In particular:¶
In general, we can conclude that to support the use case for multiple flow scheduling, the ALTO framework must be extended to satisfy the followingadditional requirements (ARs):¶
An ALTO server must provide the ANEs that are important for assessing the QoE ofthe overlay application on the path of a <source, destination> pair.¶
An ALTO server must provide information to identify how ANEs are shared on thepaths of different <source, destination> pairs.¶
An ALTO server must provide information on the properties that are importantfor assessing the QoE of the application for ANEs.¶
The extension defined in this document specifies a solution to expose suchabstract information.¶
While the problem related to multiple flow scheduling is used to help identify theadditional requirements, the extension defined in this document can be appliedto a wide range of applications. This section highlights some of the reported use cases.¶
One important use case for the Path Vector extension is to expose networkbottlenecks. Applications that need to perform large-scale data transfers canbenefit from being aware of the resource constraints exposed by this extensioneven if they have different objectives. One such example is the Worldwide LHCComputing Grid (WLCG) (where "LHC" means "Large Hadron Collider"), which is the largest example of a distributed computationcollaboration in the research and education world.¶
Figure 3 illustrates an example of using an ALTO Path Vector as an interfacebetween the job optimizer for a data analytics system and the network manager.In particular, we assume that the objective of the job optimizer is to minimize thejob completion time.¶
In such a setting, the network-aware job optimizer (e.g.,[CLARINET]) takes aquery and generates multiple query execution plans (QEPs). It can encode the QEPsas Path Vector requests that are sent to an ALTO server. The ALTO server obtainsthe routing information for the flows in a QEP and finds links, routers, ormiddleboxes (e.g., a stateful firewall) that can potentially become bottlenecksfor the QEP (e.g., see[NOVA] and[G2] for mechanisms to identify bottlenecklinks under different settings). The resource constraint information is encodedin a Path Vector response and returned to the ALTO client.¶
With the network resource constraints, the job optimizer may choose the QEP withthe optimal job completion time to be executed. It must be noted that the ALTOframework itself does not offer the capability to control the traffic. However,certain network managers may offer ways to enforce resource guarantees, such ason-demand tunnels (e.g.,[SWAN]), demand vectors (e.g.,[HUG],[UNICORN]),etc. The traffic control interfaces and mechanisms are out of scope for thisdocument.¶
Data schema Queries | | \ / +-------------+ +-----------------+ | ALTO Client | <===============> | Job Optimizer | +-------------+ +-----------------+PV | ^ PV |Request | | Response | | | On-demand resource |(Potential | | (Network allocation, demand |Data | | Resource vectors, etc. |Transfers) | | Constraints) (Non-ALTO interfaces)| v | v +-------------+ +-----------------+ | ALTO Server | <===============> | Network Manager | +-------------+ +-----------------+ / | \ | | | WAN DC1 DC2
Another example is illustrated inFigure 4. Consider a network consistingof multiple sites and a non-blocking core network, i.e., the links in the corenetwork have sufficient bandwidth that they will not become a bottleneck forthe data transfers.¶
Ongoing transfers New transfer requests \----\ | | | v v +-------------+ +---------------+ | ALTO Client | <===========> | Data Transfer | +-------------+ | Scheduler | ^ | ^ | PV Request +---------------+ | | | \--------------\ | | \--------------\ | | v PV Response | v +-------------+ +-------------+ | ALTO Server | | ALTO Server | +-------------+ +-------------+ || || +---------+ +---------+ | Network | | Network | | Manager | | Manager | +---------+ +---------+ . . . _~_ __ . . . . ( )( ) .___ ~v~v~ /--( )------------( ) ( )-----/ ( ) ( ) ~w~w~ ~^~^~^~ ~v~v~ Site 1 Non-blocking Core Site 2
With the Path Vector extension, a site can reveal the bottlenecks inside its ownnetwork with necessary information (such as link capacities) to the ALTO client,instead of providing the full topology and routing information, or no bottleneckinformation at all. The bottleneck information can be used to analyze the impactof adding/removing data transfer flows, e.g., using the framework defined in[G2]. Forexample, assume that hosts "a", "b", and "c" are in Site 1 and hosts "d", "e", and "f" are inSite 2, and there are three flows in two sites: "a -> b", "c -> d", and "e -> f" (Figure 5).¶
Site 1:[c] . ........................................> [d] +---+ 10 Gbps +---+ 10 Gbps +----+ 50 Gbps | A |---------| B |---------| GW |--------- Core +---+ +---+ +----+ ................... . . . v[a] [b]Site 2:[d] <........................................ [c] +---+ 5 Gbps +---+ 10 Gbps +----+ 20 Gbps | X |--------| Y |---------| GW |--------- Core +---+ +---+ +----+ .................... . . . v [e] [f]
Forthese flows, Site 1 returns:¶
a: { b: [ane1] },c: { d: [ane1, ane2, ane3] }ane1: bw = 10 Gbps (link: A->B)ane2: bw = 10 Gbps (link: B->GW)ane3: bw = 50 Gbps (link: GW->Core)¶and Site 2 returns:¶
c: { d: [anei, aneii, aneiii] }e: { f: [aneiv] }anei: bw = 5 Gbps (link Y->X)aneii: bw = 10 Gbps (link GW->Y)aneiii: bw = 20 Gbps (link Core->GW)aneiv: bw = 10 Gbps (link Y->GW)¶With this information, the data transfer scheduler can use algorithms such as thetheory on bottleneck structure[G2] to predict the potential throughput of theflows.¶
At the time of this writing, a growing trend in today's applications is to bring storage and computationcloser to the end users for better QoE, such as CDNs,augmented reality / virtual reality, and cloud gaming, as reported in various documents (e.g.,[SEREDGE] and[MOWIE]). ISPs may deploy multiple layers of CDN cachesor, more generally, service edges, with different latencies and available resources,including the number of CPU cores, memory, and storage.¶
For example,Figure 6 illustrates a typical edge-cloud scenario where memoryis measured in gigabytes (GB) and storage is measured in terabytes (TB). The"on-premise" edge nodes are closest to the end hosts and have the lowestlatency, and the site-radio edge node and access central office (CO) have higherlatencies but more available resources.¶
+-------------+ +----------------------+ | ALTO Client | <==========> | Application Provider | +-------------+ +----------------------+PV | ^ PV |Request | | Response | Resource allocation, | | | service establishment,(End hosts | | (Edge nodes | etc.and cloud | | and metrics) |servers) | | | v | v +-------------+ +---------------------+ | ALTO Server | <=========> | Cloud-Edge Provider | +-------------+ +---------------------+ ____________________________________/\___________ / \ | (((o | | /_\ _~_ __ __ a (/\_/\) ( ) ( )~( )_ \ /------( )---------( )----\\---( ) _|_ / (______) (___) ( ) |_| -/ Site-radio Access CO (__________) /---\ Edge Node 1 | Cloud DCOn premise | /---------/ (((o / | / Site-radio /_\ /Edge Node 2(/\_/\)-----/ /(_____)\ ___ / \ ---b--|_| -/ \--|_|--c /---\ /---\On premise On premise
With the extension defined in this document, an ALTO server can selectivelyreveal the CDNs and service edges that reside along the paths between differentend hosts and/or the cloud servers, together with their properties(e.g., storage capabilities or Graphics Processing Unit (GPU) capabilities) and available Service Level Agreement (SLA)plans. SeeFigure 7 for an example where the query is made for sources[a, b] and destinations [b, c, DC]. Here, each ANE represents a service edge, andthe properties include access latency, available resources, etc. Note that theproperties here are only used for illustration purposes and are not part of thisextension.¶
a: { b: [ane1, ane2, ane3, ane4, ane5], c: [ane1, ane2, ane3, ane4, ane6], DC: [ane1, ane2, ane3] }b: { c: [ane5, ane4, ane6], DC: [ane5, ane4, ane3] }ane1: latency = 5 ms cpu = 2 memory = 8 GB storage = 10 TB(On premise, a)ane2: latency = 20 ms cpu = 4 memory = 8 GB storage = 10 TB(Site-radio Edge Node 1)ane3: latency = 100 ms cpu = 8 memory = 128 GB storage = 100 TB(Access CO)ane4: latency = 20 ms cpu = 4 memory = 8 GB storage = 10 TB(Site-radio Edge Node 2)ane5: latency = 5 ms cpu = 2 memory = 8 GB storage = 10 TB(On premise, b)ane6: latency = 5 ms cpu = 2 memory = 8 GB storage = 10 TB(On premise, c)With the service edge information, an ALTO client may better conduct CDN requestrouting or offload functionalities from the user equipment to the service edge,with considerations in place for customized quality of experience.¶
This section provides a non-normative overview of the Path Vector extensiondefined in this document. It is assumed that readers are familiar with boththe base protocol[RFC7285] and the entity property map extension[RFC9240].¶
To satisfy the additional requirements listed inSection 4.1, this extension:¶
Thus, an ALTO client can learn about the ANEs that are important for assessing theQoE of different <source, destination> pairs by investigating the correspondingPath Vector value (AR1) and can also (1) identify common ANEs if an ANE appears in the Path Vectors of multiple <source, destination> pairs (AR2) and(2) retrieve the properties of the ANEs by searching the entity property map (AR3).¶
This extension introduces the ANE as an indirect and network-agnostic way to specifya component or an aggregation of components of a network whose properties havean impact on end-to-end performance for application traffic betweenendpoints.¶
ANEs allow ALTO servers to focus on common properties of different types ofnetwork components. For example, the throughput of a flow can be constrained bydifferent components in a network: the capacity of a physical link, the maximumthroughput of a firewall, the reserved bandwidth of an MPLS tunnel, etc. In theexample below, assume that the throughput of the firewall is 100 Mbps and thecapacity for link (A, B) is also 100 Mbps; they result in the same constraint onthe total throughput of f1 and f2. Thus, they are identical when treated as anANE.¶
f1 | ^ f1 | | -----------------> +----------+ +---+ +---+ | Firewall | | A |-----| B | +----------+ +---+ +---+ | | -----------------> v | f2 f2¶
When an ANE is defined by an ALTO server, it is assigned an identifier by theALTO server, i.e., a string of type ANEName as specified inSection 6.1,and a set of associated properties.¶
In this extension, the associations between ANEs and their properties are conveyedin an entity property map. Thus, ANEs must constitute an "entity domain" (Section 5.1 of [RFC9240]), and each ANE property must be anentity property (Section 5.2 of [RFC9240]).¶
Specifically, this document defines a new entity domain called "ane" asspecified inSection 6.2;Section 6.4 defines two initial property types for the ANEentity domain.¶
By design, ANEs are ephemeral and not to be used in further requests to otherALTO resources. More precisely, the corresponding ANE names are no longer validbeyond the scope of a Path Vector response or the incremental update streamfor a Path Vector request. Compared with globally unique ANE names, ephemeralANEs have several benefits, including better privacy for the ISP's internalstructure and more flexible ANE computation.¶
For example, an ALTO server may define an ANE for each aggregated bottlenecklink between the sources and destinations specified in the request. For requestswith different sources and destinations, the bottlenecks may be different butcan safely reuse the same ANE names. The client can still adjust its trafficbased on the information, but it is difficult to infer the underlying topology withmultiple queries.¶
However, sometimes an ISP may intend to selectively reveal some "persistent"network components that, as opposed to being ephemeral, have a longer life cycle.For example, an ALTO server may define an ANE for each service edge cluster.Once a client chooses to use a service edge, e.g., by deploying someuser-defined functions, it may want to stick to the service edge to avoid thecomplexity of state transition or synchronization, and continuously query theproperties of the edge cluster.¶
This document provides a mechanism to expose such network components aspersistent ANEs. A persistent ANE has a persistent ID that is registered in aproperty map, together with its properties. See Sections 6.2.4 and6.4.2 for more detailed instructions on how to identifyephemeral ANEs and persistent ANEs.¶
Resource-constrained ALTO clients (seeSection 4.1.2 of [RFC7285]) may benefitfrom the filtering of Path Vector query results at the ALTO server, as an ALTOclient may only require a subset of the available properties.¶
Specifically, the available properties for a given resource are announced in theInformation Resource Directory (IRD) as a new filtering capability called "ane-property-names".The properties selected by a client as being of interest are specified in thesubsequent Path Vector queries using the "ane-property-names" filter. Theresponse only includes the selected properties for the ANEs.¶
The "ane-property-names" capability for the cost map and the Endpoint Cost Serviceis specified in Sections 7.2.4 and7.3.4, respectively. The"ane-property-names" filter for the cost map and the Endpoint Cost Service is specifiedin Sections 7.2.3 and7.3.3 accordingly.¶
For an ALTO client to correctly interpret the Path Vector, this extensionspecifies a new cost type called the "Path Vector cost type".¶
The Path Vector cost type must convey both the interpretation and semantics inthe "cost-mode" and "cost-metric" parameters, respectively. Unfortunately, a single"cost-mode" value cannot fully specify the interpretation of a Path Vector,which is a compound data type. For example, in programming languages such as C++,if there existed a JSON array type named JSONArray, a Path Vector would havethe type ofJSONArray<ANEName>.¶
Instead of extending the "type system" of ALTO, this document takes a simpleand backward-compatible approach. Specifically, the "cost-mode" of the PathVector cost type is "array", which indicates that the value is a JSON array. Then, anALTO client must check the value of the "cost-metric" parameter. If the value is"ane-path", it means that the JSON array should be further interpreted as a pathof ANENames.¶
The Path Vector cost type is specified inSection 6.5.¶
For a basic ALTO information resource, a response contains only one type ofALTO resource, e.g., network map, cost map, or property map. Thus, only oneround of communication is required: an ALTO client sends a request to an ALTOserver, and the ALTO server returns a response, as shown inFigure 8.¶
ALTO client ALTO server |-------------- Request ---------------->| |<------------- Response ----------------|
The extension defined in this document, on the other hand, involves two types ofinformation resources: Path Vectors conveyed in an InfoResourceCostMap data component (definedinSection 11.2.3.6 of [RFC7285]) or an InfoResourceEndpointCostMap data component (definedinSection 11.5.1.6 of [RFC7285]), and ANE properties conveyed in anInfoResourceProperties data component (defined inSection 7.6 of [RFC9240]).¶
Instead of two consecutive message exchanges, the extension defined in thisdocument enforces one round of communication. Specifically, the ALTO client mustinclude the source and destination pairs and the requested ANE properties in asingle request, and the ALTO server must return a single response containingboth the Path Vectors and properties associated with the ANEs in the PathVectors, as shown inFigure 9. Since the two parts are bundled together in oneresponse message, their orders are interchangeable. See Sections 7.2.6 and7.3.6 for details.¶
ALTO client ALTO server |------------- PV Request -------------->| |<----- PV Response (Cost Map Part) -----| |<--- PV Response (Property Map Part) ---|
This design is based on the following considerations:¶
One approach for realizing the one-round communication is to define a new mediatype to contain both objects, but this violates modular design. This documentfollows the standard-conforming usage of the "multipart/related" media type as definedin[RFC2387] to elegantly combine the objects. Path Vectors are encoded in anInfoResourceCostMap data component or InfoResourceEndpointCostMap data component, and the property map isencoded in an InfoResourceProperties data component. They are encapsulated as parts of amultipart message. This modular composition allows ALTO servers and clients toreuse the data models of the existing information resources. Specifically, thisdocument addresses the following practical issues using "multipart/related".¶
ALTO uses a media type to indicate the type of an entry in the IRD (e.g., "application/alto-costmap+json" for the cost mapand "application/alto-endpointcost+json" for the Endpoint Cost Service). Simplyusing "multipart/related" as the media type, however, makes it impossiblefor an ALTO client to identify the type of service provided by relatedentries.¶
To address this issue, this document uses the "type" parameter to indicate theobject root of a multipart/related message. For a cost map resource, the"media-type" field in the IRD entry is "multipart/related" with the parameter"type=application/alto-costmap+json"; for an Endpoint Cost Service, theparameter is "type=application/alto-endpointcost+json".¶
As the response of a Path Vector resource is a multipart message with twodifferent parts, it is important that each part can be uniquely identified.Following the design provided in[RFC8895], this extension requires that an ALTOserver assign a unique identifier to each part of the multipart responsemessage. This identifier, referred to as a Part Resource ID (seeSection 6.6 for details), is present in the part message's "Content-ID"header field. By concatenating the Part Resource ID to the identifier of the PathVector request, an ALTO server/client can uniquely identify the Path Vector partor the property map part.¶
An ANE name is encoded as a JSON string with the same format as that of the typePIDName (Section 10.1 of [RFC7285]).¶
The type ANEName is used in this document to indicate a string of thisformat.¶
The ANE entity domain associates property values with the ANEs in a property map. Accordingly, the ANE entity domain always depends ona property map.¶
It must be noted that the term "domain" here does not refer to a network domain.Rather, it is inherited from the entity domain as defined inSection 3.2 of [RFC9240]; the entity domain represents the set of valid entitiesdefined by an ALTO information resource (called the "defining informationresource").¶
The entity domain type is "ane".¶
The entity identifiers are the ANE names in the associated property map.¶
There is no hierarchy or inheritance for properties associated with ANEs.¶
The defining resource for entity domain type "ane"MUST be a property map, i.e.,the media type of defining resources is:¶
application/alto-propmap+json¶
Specifically, for ephemeral ANEs that appear in a Path Vector response, theirentity domain namesMUST be exactly ".ane", and the defining resource of theseANEs is the property map part of the multipart response. Meanwhile, for anypersistent ANE whose defining resource is a property map resource, its entitydomain nameMUST have the format of "PROPMAP.ane", where PROPMAP is the resourceID of the defining resource. Persistent entities are "persistent" becausestandalone queries can be made by an ALTO client to their defining resource(s)when the connection to the Path Vector service is closed.¶
For example, the defining resource of an ephemeral ANE whose entity identifieris ".ane:NET1" is the property map part that contains this identifier. Thedefining resource of a persistent ANE whose entity identifier is"dc-props.ane:DC1" is the property map with the resource ID "dc-props".¶
An ANE property name is encoded as a JSON string with the same format as that of anentity property name (Section 5.2.2 of [RFC9240]).¶
Two initial ANE property types are specified: "max-reservable-bandwidth" and"persistent-entity-id".¶
Note that these property types do not depend on any information resources. Assuch, the "EntityPropertyName" parameterMUST only have the EntityPropertyType part.¶
The maximum reservable bandwidth property ("max-reservable-bandwidth") standsfor the maximum bandwidth that can be reserved for all the traffic thattraverses an ANE. The valueMUST be encoded as a non-negative numerical costvalue as defined inSection 6.1.2.1 of [RFC7285], and the unit is bits persecond (bps). If this property is requested by the ALTO client but is not presentfor an ANE in the server response, itMUST be interpreted as meaning that the propertyis not defined for the ANE.¶
This property can be offered in a setting where the ALTO server is part of anetwork system that provides on-demand resource allocation and the ALTO clientis part of a user application. One existing example is[NOVA]: the ALTO serveris part of a Software-Defined Networking (SDN) controller and exposes a list of traversed network elementsand associated link bandwidth to the client. The encoding in[NOVA] differsfrom the Path Vector response defined in this document in that the Path Vector partand property map part are placed in the same JSON object.¶
In such a framework, the ALTO server exposes resourceavailability information (e.g., reservable bandwidth) to the ALTO client. How the client makes resourcerequests based on the information, and how the resource allocation is achieved,respectively, depend on interfaces between the management system and the users ora higher-layer protocol (e.g., SDN network intents[INTENT-BASED-NETWORKING] or MPLS tunnels), which areout of scope for this document.¶
This document enables the discovery of a persistent ANE by exposing itsentity identifier as the persistent entity ID property of an ephemeral ANE in the pathvector response. The value of this property is encoded with the EntityID format defined inSection 5.1.3 of [RFC9240].¶
In this format, the entity ID combines:¶
With this format, the client has all the needed information for furtherstandalone query properties on the persistent ANE.¶
To illustrate the use of "max-reservable-bandwidth", consider the followingnetwork with five nodes. Assume that the client wants to query the maximum reservablebandwidth from H1 to H2. An ALTO server may split the network into two ANEs:"ane1", which represents the subnetwork with routers A, B, and C; and "ane2", whichrepresents the subnetwork with routers B, D, and E. The maximum reservablebandwidth for "ane1" is 15 Mbps (using path A->C->B), and the maximum reservablebandwidth for "ane2" is 20 Mbps (using path B->D->E).¶
20 Mbps 20 Mbps 10 Mbps +---+ +---+ +---+ /----| B |---| D |----| E |---- H2 +---+/ +---+ +---+ +---+H1 ----| A | 15 Mbps| +---+\ +---+ \----| C | 15 Mbps +---+¶
To illustrate the use of "persistent-entity-id", consider the scenario inFigure 6. As the life cycles of service edges are typically long, the service edges maycontain information that is not specific to the query. Such information can bestored in an individual entity property map and can later be accessed by an ALTOclient.¶
For example, "ane1" inFigure 7 represents the on-premise service edgeclosest to host "a". Assume that the properties of the service edges are provided inan entity property map called "se-props" and the ID of the on-premise serviceedge is "9a0b55f7-7442-4d56-8a2c-b4cc6a8e3aa1"; the "persistent-entity-id" setting for"ane1" will be "se-props.ane:9a0b55f7-7442-4d56-8a2c-b4cc6a8e3aa1". With thispersistent entity ID, an ALTO client may send queries to the "se-props" resourcewith the entity ID ".ane:9a0b55f7-7442-4d56-8a2c-b4cc6a8e3aa1".¶
This document defines a new cost type, which is referred to as the Path Vectorcost type. An ALTO serverMUST offer this cost type if it supports the extensiondefined in this document.¶
The cost metric "ane-path" indicates that the value of such a cost type conveys anarray of ANE names, where each ANE name uniquely represents an ANE traversed bytraffic from a source to a destination.¶
An ALTO clientMUST interpret the Path Vector as if the traffic between a sourceand a destination logically traverses the ANEs in the same order as they appearin the Path Vector.¶
When the Path Vector procedures defined in this document are in use, an ALTOserver using the "ane-path" cost metric and the "array" cost mode (seeSection 6.5.2)MUST return as the cost value a JSON array of data type ANEName, and theclientMUST also check that each element contained in the array is an ANEName(Section 6.1). Otherwise, the clientMUST discard the response andSHOULDfollow the guidance inSection 8.3.4.3 of [RFC7285] to handle the error.¶
The cost mode "array" indicates that every cost value in the response body of a(filtered) cost map or an Endpoint Cost ServiceMUST be interpreted as a JSONarray object. While this cost mode can be applied to all cost metrics,additional specifications will be needed to clarify the semantics of the "array"cost mode when combined with cost metrics other than "ane-path".¶
A Part Resource ID is encoded as a JSON string with the same format as that of thetype ResourceID (Section 10.2 of [RFC7285]).¶
Even though the "client-id" assigned to a Path Vector request and the PartResource IDMAY contain up to 64 characters by their own definition, theirconcatenation (seeSection 5.3.2)MUST also conform to the same lengthconstraint. The same requirement applies to the resource ID of the Path Vectorresource, too. Thus, it isRECOMMENDED to limit the length of the resource ID andclient ID related to a Path Vector resource to 31 characters.¶
A Part Content ID conforms to the format of "msg-id" as specified in[RFC2387] and[RFC5322]. Specifically, it has the following format:¶
"<" PART-RESOURCE-ID "@" DOMAIN-NAME ">"¶
PART-RESOURCE-ID has the same format as the Part Resource ID. It is used toidentify whether a part message is a Path Vector or a property map.¶
DOMAIN-NAME has the same format as "dot-atom-text" as specified inSection 3.2.3 of [RFC5322]. It must be the domain name of the ALTO server.¶
This document uses the same syntax and notation as those introduced inSection 8.2 of [RFC7285] to specify the extensions to existing ALTO resources andservices.¶
This document introduces a new ALTO resource called the "multipart filtered cost mapresource", which allows an ALTO server to provide other ALTO resources associatedwith the cost map resource in the same response.¶
The media type of the multipart filtered cost map resource is"multipart/related", and the required "type" parameterMUST havea value of "application/alto-costmap+json".¶
The multipart filtered cost map is requested using the HTTP POST method.¶
The input parameters of the multipart filtered cost map are supplied in the bodyof an HTTP POST request. This document extends the input parameters to afiltered cost map, which is defined as a JSON object of typeReqFilteredCostMap inSection 4.1.2 of [RFC8189], with a dataformat indicated by the media type "application/alto-costmapfilter+json", whichis a JSON object of type PVReqFilteredCostMap:¶
object { [EntityPropertyName ane-property-names<0..*>;]} PVReqFilteredCostMap : ReqFilteredCostMap;¶with field:¶
This field provides a list of selected ANE properties to be included in the response. Eachproperty in this listMUST match one of the supported ANE properties indicatedin the resource's "ane-property-names" capability (Section 7.2.4). If thefield is not present, itMUST be interpreted as an empty list.¶
Example: Consider the network inFigure 1. If an ALTO client wants toquery the "max-reservable-bandwidth" setting between PID1 and PID2, it can submit thefollowing request.¶
POST /costmap/pv HTTP/1.1 Host: alto.example.com Accept: multipart/related;type=application/alto-costmap+json, application/alto-error+json Content-Length: 212 Content-Type: application/alto-costmapfilter+json { "cost-type": { "cost-mode": "array", "cost-metric": "ane-path" }, "pids": { "srcs": [ "PID1" ], "dsts": [ "PID2" ] }, "ane-property-names": [ "max-reservable-bandwidth" ] }¶The multipart filtered cost map resource extends the capabilities definedinSection 4.1.1 of [RFC8189]. The capabilities are defined by a JSONobject of type PVFilteredCostMapCapabilities:¶
object { [EntityPropertyName ane-property-names<0..*>;]} PVFilteredCostMapCapabilities : FilteredCostMapCapabilities;¶with field:¶
This field provides a list of ANE properties that can be returned. If the field is notpresent, itMUST be interpreted as an empty list, indicating that the ALTO servercannot provide any ANE properties.¶
This extension also introduces additional restrictions for the following fields:¶
The "cost-type-names" fieldMUST include the Path Vector cost type,unless explicitly documented by a future extension. This also implies that thePath Vector cost typeMUST be defined in the "cost-types" of the IRD's "meta" field.¶
If the "cost-type-names" field includes the Path Vector cost type,the "cost-constraints" fieldMUST be either "false" or not present,unless specificallyinstructed by a future document.¶
If the "cost-type-names" field includes the Path Vector cost type and the"testable-cost-type-names" field is present, the Path Vector cost typeMUST NOT be included in the "testable-cost-type-names" field unless specificallyinstructed by a future document.¶
This memberMUST include the resource ID of the network map based on which thePIDs are defined. If this resource supports "persistent-entity-id", itMUST alsoinclude the defining resources of persistent ANEs that may appear in the response.¶
The responseMUST indicate an error, using ALTO Protocol error handling asdefined inSection 8.5 of [RFC7285], if the request is invalid.¶
The "Content-Type" header field of the responseMUST be "multipart/related" as definedby[RFC2387], with the following parameters:¶
The "type" parameter is mandatory andMUST be "application/alto-costmap+json". Notethat[RFC2387] permits parameters both with and without double quotes.¶
The "start" parameter is as defined in[RFC2387] and is optional.If present, itMUST have the same value as the "Content-ID" header field of the PathVector part.¶
The "boundary" parameter is as defined inSection 5.1.1 of [RFC2046] and is mandatory.¶
The body of the responseMUST consist of two parts:¶
The Path Vector partMUST include "Content-ID" and "Content-Type" in itsheader. The "Content-Type"MUST be "application/alto-costmap+json".The value of "Content-ID"MUST have the same format as the Part Content ID asspecified inSection 6.6.¶
The body of the Path Vector partMUST be a JSON object with the same format as thatdefined inSection 11.2.3.6 of [RFC7285] when the "cost-type" field ispresent in the input parameters andMUST be a JSON object with the same formatas that defined inSection 4.1.3 of [RFC8189] if the "multi-cost-types" field ispresent. The JSON objectMUST include the"vtag" field in the "meta" field, which provides the version tag of thereturned CostMapData object. The resource ID of the version tagMUST follow theformat of¶
resource-id '.' part-resource-id¶
where "resource-id" is the resource ID of the Path Vector resource and"part-resource-id" has the same value as the PART-RESOURCE-ID in the"Content-ID" of the Path Vector part.The "meta" fieldMUST also include the "dependent-vtags" field, whose value isa single-element array to indicate the version tag of the network map used,where the network map is specified in the "uses" attribute of the multipartfiltered cost map resource in the IRD.¶
The entity property map partMUST also include "Content-ID" and"Content-Type" in its header. The "Content-Type"MUST be"application/alto-propmap+json". The value of "Content-ID"MUST have the sameformat as the Part Content ID as specified inSection 6.6.¶
The body of the entity property map part is a JSON object with the sameformat as that defined inSection 7.6 of [RFC9240]. TheJSON objectMUST include the "dependent-vtags" field in the "meta" field. Thevalue of the "dependent-vtags" fieldMUST be an array of VersionTag objects asdefined bySection 10.3 of [RFC7285]. The "vtag" of the Path Vector partMUSTbe included in the "dependent-vtags" field. If "persistent-entity-id" is requested, theversion tags of the dependent resources that may expose the entities in theresponseMUST also be included.¶
The PropertyMapData object has one member for each ANEName that appears in the PathVector part, which is an entity identifier belonging to the self-definedentity domain as defined inSection 5.1.2.3 of [RFC9240]. The EntityProps object for each ANE has onemember for each property that is both 1) associated with the ANE and 2)specified in the "ane-property-names" field in the request. If the Path Vector costtype is not included in the "cost-type" field or the "multi-cost-type" field,the "property-map" fieldMUST be present and the valueMUST be an empty object({}).¶
A complete and valid responseMUST include both the Path Vector part and theproperty map part in the multipart message. If any part isnot present, theclientMUST discard the received information and send another request ifnecessary.¶
The Path Vector part, whose media type is the same as the "type" parameter of the multipart response message, is the root body part as defined in[RFC2387]. Thus, it is the element that the application processes first. Even though the"start" parameter allows it to be placed anywhere in the part sequence, it isRECOMMENDED that the parts arrive in the same order as they are processed, i.e.,the Path Vector part is always placed as the first part, followed by the propertymap part. When doing so, an ALTO serverMAY choose not to set the "start"parameter, which implies that the first part is the object root.¶
Example: Consider the network inFigure 1. The response to the examplerequest inSection 7.2.3 is as follows, where "ANE1" represents theaggregation of all the switches in the network.¶
HTTP/1.1 200 OKContent-Length: 911Content-Type: multipart/related; boundary=example-1; type=application/alto-costmap+json--example-1Content-ID: <costmap@alto.example.com>Content-Type: application/alto-costmap+json{ "meta": { "vtag": { "resource-id": "filtered-cost-map-pv.costmap", "tag": "fb20b76204814e9db37a51151faaaef2" }, "dependent-vtags": [ { "resource-id": "my-default-networkmap", "tag": "75ed013b3cb58f896e839582504f6228" } ], "cost-type": { "cost-mode": "array", "cost-metric": "ane-path" } }, "cost-map": { "PID1": { "PID2": [ "ANE1" ] } }}--example-1Content-ID: <propmap@alto.example.com>Content-Type: application/alto-propmap+json{ "meta": { "dependent-vtags": [ { "resource-id": "filtered-cost-map-pv.costmap", "tag": "fb20b76204814e9db37a51151faaaef2" } ] }, "property-map": { ".ane:ANE1": { "max-reservable-bandwidth": 100000000 } }}--example-1¶This document introduces a new ALTO resource called the "multipart Endpoint CostService", which allows an ALTO server to provide other ALTO resources associatedwith the Endpoint Cost Service resource in the same response.¶
The media type of the multipart Endpoint Cost Service resource is"multipart/related", and the required "type" parameterMUST havea value of "application/alto-endpointcost+json".¶
The multipart Endpoint Cost Service resource is requested using the HTTP POST method.¶
The input parameters of the multipart Endpoint Cost Service resource aresupplied in the body of an HTTP POST request. This document extends the inputparameters to an Endpoint Cost Service, which is defined as a JSON object oftype ReqEndpointCostMap inSection 4.2.2 of [RFC8189], with a dataformat indicated by the media type "application/alto-endpointcostparams+json",which is a JSON object of type PVReqEndpointCostMap:¶
object { [EntityPropertyName ane-property-names<0..*>;]} PVReqEndpointCostMap : ReqEndpointCostMap;¶with field:¶
This document defines the "ane-property-names" field in PVReqEndpointCostMap as being thesame as in PVReqFilteredCostMap. SeeSection 7.2.3.¶
Example: Consider the network inFigure 1. If an ALTO client wants toquery the "max-reservable-bandwidth" setting between "eh1" and "eh2", it can submit thefollowing request.¶
POST /ecs/pv HTTP/1.1Host: alto.example.comAccept: multipart/related;type=application/alto-endpointcost+json, application/alto-error+jsonContent-Length: 238Content-Type: application/alto-endpointcostparams+json{ "cost-type": { "cost-mode": "array", "cost-metric": "ane-path" }, "endpoints": { "srcs": [ "ipv4:192.0.2.2" ], "dsts": [ "ipv4:192.0.2.18" ] }, "ane-property-names": [ "max-reservable-bandwidth" ]}¶The capabilities of the multipart Endpoint Cost Service resource are defined bya JSON object of type PVEndpointCostCapabilities, which is defined as being the sameas PVFilteredCostMapCapabilities. SeeSection 7.2.4.¶
If this resource supports "persistent-entity-id", itMUST also include thedefining resources of persistent ANEs that may appear in the response.¶
The responseMUST indicate an error, using ALTO Protocol error handling asdefined inSection 8.5 of [RFC7285], if the request is invalid.¶
The "Content-Type" header field of the responseMUST be "multipart/related" as definedby[RFC2387], with the following parameters:¶
The "type" parameterMUST be "application/alto-endpointcost+json" and is mandatory.¶
The "start" parameter is as defined inSection 7.2.6.¶
The "boundary" parameter is as defined inSection 5.1.1 of [RFC2046] and is mandatory.¶
The body of the responseMUST consist of two parts:¶
The Path Vector partMUST include "Content-ID" and "Content-Type" in itsheader.The "Content-Type"MUST be "application/alto-endpointcost+json".The value of "Content-ID"MUST have the same format as the Part Content ID asspecified inSection 6.6.¶
The body of the Path Vector partMUST be a JSON object with the same format as thatdefined inSection 11.5.1.6 of [RFC7285] when the "cost-type" field ispresent in the input parameters andMUST be a JSON object with the same formatas that defined inSection 4.2.3 of [RFC8189] if the "multi-cost-types" field ispresent. The JSON objectMUST include the"vtag" field in the "meta" field, which provides the version tag of the returnedEndpointCostMapData object. The resource ID of the version tagMUST follow the format of¶
resource-id '.' part-resource-id¶
where "resource-id" is the resource ID of the Path Vector resource and"part-resource-id" has the same value as the PART-RESOURCE-ID in the "Content-ID"of the Path Vector part.¶
The entity property map partMUST also include "Content-ID" and"Content-Type" in its header. The "Content-Type"MUST be"application/alto-propmap+json".The value of "Content-ID"MUST have the same format as the Part Content ID asspecified inSection 6.6.¶
The body of the entity property map partMUST be a JSON object with the sameformat as that defined inSection 7.6 of [RFC9240]. TheJSON objectMUST include the "dependent-vtags" field in the "meta" field. Thevalue of the "dependent-vtags" fieldMUST be an array of VersionTag objects asdefined bySection 10.3 of [RFC7285]. The "vtag" of the Path Vector partMUSTbe included in the "dependent-vtags" field. If "persistent-entity-id" is requested, theversion tags of the dependent resources that may expose the entities in theresponseMUST also be included.¶
The PropertyMapData object has one member for each ANEName that appears in the PathVector part, which is an entity identifier belonging to the self-definedentity domain as defined inSection 5.1.2.3 of [RFC9240]. The EntityProps object for each ANE has onemember for each property that is both 1) associated with the ANE and 2)specified in the "ane-property-names" field in the request. If the Path Vector costtype is not included in the "cost-type" field or the "multi-cost-type" field,the "property-map" fieldMUST be present and the valueMUST be an empty object({}).¶
A complete and valid responseMUST include both the Path Vector part and theproperty map part in the multipart message. If any part isnot present, theclientMUST discard the received information and send another request ifnecessary.¶
The Path Vector part, whose media type is the same as the "type" parameter of the multipart response message, is the root body part as defined in[RFC2387]. Thus, it is the element that the application processes first. Even though the"start" parameter allows it to be placed anywhere in the part sequence, it isRECOMMENDED that the parts arrive in the same order as they are processed, i.e.,the Path Vector part is always placed as the first part, followed by the propertymap part. When doing so, an ALTO serverMAY choose not to set the "start"parameter, which implies that the first part is the object root.¶
Example: Consider the network inFigure 1. The response to the examplerequest inSection 7.3.3 is as follows.¶
HTTP/1.1 200 OKContent-Length: 899Content-Type: multipart/related; boundary=example-1; type=application/alto-endpointcost+json--example-1Content-ID: <ecs@alto.example.com>Content-Type: application/alto-endpointcost+json{ "meta": { "vtag": { "resource-id": "ecs-pv.ecs", "tag": "ec137bb78118468c853d5b622ac003f1" }, "dependent-vtags": [ { "resource-id": "my-default-networkmap", "tag": "677fe5f4066848d282ece213a84f9429" } ], "cost-type": { "cost-mode": "array", "cost-metric": "ane-path" } }, "cost-map": { "ipv4:192.0.2.2": { "ipv4:192.0.2.18": [ "ANE1" ] } }}--example-1Content-ID: <propmap@alto.example.com>Content-Type: application/alto-propmap+json{ "meta": { "dependent-vtags": [ { "resource-id": "ecs-pv.ecs", "tag": "ec137bb78118468c853d5b622ac003f1" } ] }, "property-map": { ".ane:ANE1": { "max-reservable-bandwidth": 100000000 } }}--example-1¶This section lists some examples of Path Vector queries and the correspondingresponses. Some long lines are truncated for better readability.¶
Figure 10 illustrates the network properties and thus the message contents. Thereare three subnetworks (NET1, NET2, and NET3) and two interconnection links (L1 andL2). It is assumed that each subnetwork has sufficiently large bandwidth to bereserved.¶
----- L1 / PID1 +----------+ 10 Gbps +----------+ PID3 192.0.2.0/28+-+ +------+ +---------+ +--+192.0.2.32/28 | | MEC1 | | | | 2001:db8::3:0/16 | +------+ | +-----+ | PID2 | | | +----------+192.0.2.16/28+-+ | | NET3 | | | 15 Gbps | | | \ +----------+ | -------- L2 NET1 | +----------+ | +------+ | PID4 | | MEC2 | +--+192.0.2.48/28 | +------+ | 2001:db8::4:0/16 +----------+ NET2
To give a comprehensive example of the extension defined in this document, weconsider the network inFigure 10. Assume that the ALTO server provides thefollowing information resources:¶
Below is the IRD of the example ALTO server. Toenable the extension defined in this document, the Path Vector cost type(Section 6.5), represented by "path-vector" below,is defined in the "cost-types" of the "meta" field and isincluded in the "cost-type-names" of resources "filtered-cost-map-pv" and"endpoint-cost-pv".¶
{ "meta": { "cost-types": { "path-vector": { "cost-mode": "array", "cost-metric": "ane-path" }, "num-rc": { "cost-mode": "numerical", "cost-metric": "routingcost" } } }, "resources": { "my-default-networkmap": { "uri": "https://alto.example.com/networkmap", "media-type": "application/alto-networkmap+json" }, "filtered-cost-map-pv": { "uri": "https://alto.example.com/costmap/pv", "media-type": "multipart/related; type=application/alto-costmap+json", "accepts": "application/alto-costmapfilter+json", "capabilities": { "cost-type-names": [ "path-vector" ], "ane-property-names": [ "max-reservable-bandwidth" ] }, "uses": [ "my-default-networkmap" ] }, "ane-props": { "uri": "https://alto.example.com/ane-props", "media-type": "application/alto-propmap+json", "accepts": "application/alto-propmapparams+json", "capabilities": { "mappings": { ".ane": [ "cpu" ] } } }, "endpoint-cost-pv": { "uri": "https://alto.exmaple.com/endpointcost/pv", "media-type": "multipart/related; type=application/alto-endpointcost+json", "accepts": "application/alto-endpointcostparams+json", "capabilities": { "cost-type-names": [ "path-vector" ], "ane-property-names": [ "max-reservable-bandwidth", "persistent-entity-id" ] }, "uses": [ "ane-props" ] }, "update-pv": { "uri": "https://alto.example.com/updates/pv", "media-type": "text/event-stream", "uses": [ "endpoint-cost-pv" ], "accepts": "application/alto-updatestreamparams+json", "capabilities": { "support-stream-control": true } }, "multicost-pv": { "uri": "https://alto.exmaple.com/endpointcost/mcpv", "media-type": "multipart/related; type=application/alto-endpointcost+json", "accepts": "application/alto-endpointcostparams+json", "capabilities": { "cost-type-names": [ "path-vector", "num-rc" ], "max-cost-types": 2, "testable-cost-type-names": [ "num-rc" ], "ane-property-names": [ "max-reservable-bandwidth", "persistent-entity-id" ] }, "uses": [ "ane-props" ] } }}¶The following examples demonstrate the request to the "filtered-cost-map-pv"resource and the corresponding response.¶
The request uses the "path-vector" cost type in the "cost-type" field. The"ane-property-names" field is missing, indicating that the client only requeststhe Path Vector and not the ANE properties.¶
The response consists of two parts:¶
POST /costmap/pv HTTP/1.1Host: alto.example.comAccept: multipart/related;type=application/alto-costmap+json, application/alto-error+jsonContent-Length: 163Content-Type: application/alto-costmapfilter+json{ "cost-type": { "cost-mode": "array", "cost-metric": "ane-path" }, "pids": { "srcs": [ "PID1" ], "dsts": [ "PID3", "PID4" ] }}¶HTTP/1.1 200 OKContent-Length: 952Content-Type: multipart/related; boundary=example-1; type=application/alto-costmap+json--example-1Content-ID: <costmap@alto.example.com>Content-Type: application/alto-costmap+json{ "meta": { "vtag": { "resource-id": "filtered-cost-map-pv.costmap", "tag": "d827f484cb66ce6df6b5077cb8562b0a" }, "dependent-vtags": [ { "resource-id": "my-default-networkmap", "tag": "c04bc5da49534274a6daeee8ea1dec62" } ], "cost-type": { "cost-mode": "array", "cost-metric": "ane-path" } }, "cost-map": { "PID1": { "PID3": [ "L1" ], "PID4": [ "L1", "L2" ] } }}--example-1Content-ID: <propmap@alto.example.com>Content-Type: application/alto-propmap+json{ "meta": { "dependent-vtags": [ { "resource-id": "filtered-cost-map-pv.costmap", "tag": "d827f484cb66ce6df6b5077cb8562b0a" } ] }, "property-map": { ".ane:L1": {}, ".ane:L2": {} }}--example-1¶The following examples demonstrate the request to the "endpoint-cost-pv"resource and the corresponding response.¶
The request uses the "path-vector" cost type in the "cost-type" field andqueries the maximum reservable bandwidth ANE property and the persistent entity IDproperty for two IPv4 source and destination pairs (192.0.2.34 -> 192.0.2.2 and192.0.2.34 -> 192.0.2.50) and one IPv6 source and destination pair(2001:db8::3:1 -> 2001:db8::4:1).¶
The response consists of two parts:¶
Both NET1 and NET2 have a mobile edge deployed, i.e., MEC1 in NET1 and MEC2 inNET2. Assume that the ANEName values for MEC1 and MEC2 are "MEC1" and "MEC2" and theirproperties can be retrieved from the property map "ane-props". Thus, the"persistent-entity-id" property values for NET1 and NET2 are "ane-props.ane:MEC1" and"ane-props.ane:MEC2", respectively.¶
POST /endpointcost/pv HTTP/1.1Host: alto.example.comAccept: multipart/related; type=application/alto-endpointcost+json, application/alto-error+jsonContent-Length: 383Content-Type: application/alto-endpointcostparams+json{ "cost-type": { "cost-mode": "array", "cost-metric": "ane-path" }, "endpoints": { "srcs": [ "ipv4:192.0.2.34", "ipv6:2001:db8::3:1" ], "dsts": [ "ipv4:192.0.2.2", "ipv4:192.0.2.50", "ipv6:2001:db8::4:1" ] }, "ane-property-names": [ "max-reservable-bandwidth", "persistent-entity-id" ]}¶HTTP/1.1 200 OKContent-Length: 1508Content-Type: multipart/related; boundary=example-2; type=application/alto-endpointcost+json--example-2Content-ID: <ecs@alto.example.com>Content-Type: application/alto-endpointcost+json{ "meta": { "vtags": { "resource-id": "endpoint-cost-pv.ecs", "tag": "bb6bb72eafe8f9bdc4f335c7ed3b10822a391cef" }, "cost-type": { "cost-mode": "array", "cost-metric": "ane-path" } }, "endpoint-cost-map": { "ipv4:192.0.2.34": { "ipv4:192.0.2.2": [ "NET3", "L1", "NET1" ], "ipv4:192.0.2.50": [ "NET3", "L2", "NET2" ] }, "ipv6:2001:db8::3:1": { "ipv6:2001:db8::4:1": [ "NET3", "L2", "NET2" ] } }}--example-2Content-ID: <propmap@alto.example.com>Content-Type: application/alto-propmap+json{ "meta": { "dependent-vtags": [ { "resource-id": "endpoint-cost-pv.ecs", "tag": "bb6bb72eafe8f9bdc4f335c7ed3b10822a391cef" }, { "resource-id": "ane-props", "tag": "bf3c8c1819d2421c9a95a9d02af557a3" } ] }, "property-map": { ".ane:NET1": { "max-reservable-bandwidth": 50000000000, "persistent-entity-id": "ane-props.ane:MEC1" }, ".ane:NET2": { "max-reservable-bandwidth": 50000000000, "persistent-entity-id": "ane-props.ane:MEC2" }, ".ane:NET3": { "max-reservable-bandwidth": 50000000000 }, ".ane:L1": { "max-reservable-bandwidth": 10000000000 }, ".ane:L2": { "max-reservable-bandwidth": 15000000000 } }}--example-2¶In certain scenarios where the traversal order is not crucial, an ALTO serverimplementation may choose not to strictly follow the physical traversal orderand may even obfuscate the order intentionally to preserve its own privacy orconform to its own policies.For example, an ALTO server may choose to aggregate NET1 and L1 as a new ANEwith ANE name "AGGR1" and aggregate NET2 and L2 as a new ANE with ANE name"AGGR2". The "max-reservable-bandwidth" property of "AGGR1" takes the value of L1, whichis smaller than that of NET1, and the "persistent-entity-id" property of "AGGR1" takesthe value of NET1. The properties of "AGGR2" are computed in a similar way;the obfuscated response is as shown below. Note that the obfuscation of PathVector responses is implementation specific and is out of scope for thisdocument. Developers may refer toSection 11 for further references.¶
HTTP/1.1 200 OKContent-Length: 1333Content-Type: multipart/related; boundary=example-2; type=application/alto-endpointcost+json--example-2Content-ID: <ecs@alto.example.com>Content-Type: application/alto-endpointcost+json{ "meta": { "vtags": { "resource-id": "endpoint-cost-pv.ecs", "tag": "bb975862fbe3422abf4dae386b132c1d" }, "cost-type": { "cost-mode": "array", "cost-metric": "ane-path" } }, "endpoint-cost-map": { "ipv4:192.0.2.34": { "ipv4:192.0.2.2": [ "NET3", "AGGR1" ], "ipv4:192.0.2.50": [ "NET3", "AGGR2" ] }, "ipv6:2001:db8::3:1": { "ipv6:2001:db8::4:1": [ "NET3", "AGGR2" ] } }}--example-2Content-ID: <propmap@alto.example.com>Content-Type: application/alto-propmap+json{ "meta": { "dependent-vtags": [ { "resource-id": "endpoint-cost-pv.ecs", "tag": "bb975862fbe3422abf4dae386b132c1d" }, { "resource-id": "ane-props", "tag": "bf3c8c1819d2421c9a95a9d02af557a3" } ] }, "property-map": { ".ane:AGGR1": { "max-reservable-bandwidth": 10000000000, "persistent-entity-id": "ane-props.ane:MEC1" }, ".ane:AGGR2": { "max-reservable-bandwidth": 15000000000, "persistent-entity-id": "ane-props.ane:MEC2" }, ".ane:NET3": { "max-reservable-bandwidth": 50000000000 } }}--example-2¶In this example, an ALTO client subscribes to the incremental update for themultipart Endpoint Cost Service resource "endpoint-cost-pv".¶
POST /updates/pv HTTP/1.1Host: alto.example.comAccept: text/event-streamContent-Type: application/alto-updatestreamparams+jsonContent-Length: 120{ "add": { "ecspvsub1": { "resource-id": "endpoint-cost-pv", "input": <ecs-input> } }}¶Based on the server-side process defined in[RFC8895], the ALTO server willsend the "control-uri" first, using a Server-Sent Event (SSE) followed by the fullresponse of the multipart message.¶
HTTP/1.1 200 OKConnection: keep-aliveContent-Type: text/event-streamevent: application/alto-updatestreamcontrol+jsondata: {"control-uri": "https://alto.example.com/updates/streams/123"}event: multipart/related;boundary=example-3; type=application/alto-endpointcost+json,ecspvsub1data: --example-3data: Content-ID: <ecsmap@alto.example.com>data: Content-Type: application/alto-endpointcost+jsondata:data: <endpoint-cost-map-entry>data: --example-3data: Content-ID: <propmap@alto.example.com>data: Content-Type: application/alto-propmap+jsondata:data: <property-map-entry>data: --example-3--¶When the contents change, the ALTO server will publish the updates for each nodein this tree separately, based onSection 6.7.3 of [RFC8895].¶
event: application/merge-patch+json, ecspvsub1.ecsmap@alto.example.comdata: <Merge patch for endpoint-cost-map-update>event: application/merge-patch+json, ecspvsub1.propmap@alto.example.comdata: <Merge patch for property-map-update>¶
The following examples demonstrate the request to the "multicost-pv" resourceand the corresponding response.¶
The request asks for two cost types: the first is the Path Vector cost type, andthe second is a numerical routing cost. It also queries the maximum reservablebandwidth ANE property and the persistent entity ID property for two IPv4 source anddestination pairs (192.0.2.34 -> 192.0.2.2 and 192.0.2.34 -> 192.0.2.50) and oneIPv6 source and destination pair (2001:db8::3:1 -> 2001:db8::4:1).¶
The response consists of two parts:¶
POST /endpointcost/mcpv HTTP/1.1Host: alto.example.comAccept: multipart/related; type=application/alto-endpointcost+json, application/alto-error+jsonContent-Length: 454Content-Type: application/alto-endpointcostparams+json{ "multi-cost-types": [ { "cost-mode": "array", "cost-metric": "ane-path" }, { "cost-mode": "numerical", "cost-metric": "routingcost" } ], "endpoints": { "srcs": [ "ipv4:192.0.2.34", "ipv6:2001:db8::3:1" ], "dsts": [ "ipv4:192.0.2.2", "ipv4:192.0.2.50", "ipv6:2001:db8::4:1" ] }, "ane-property-names": [ "max-reservable-bandwidth", "persistent-entity-id" ]}¶HTTP/1.1 200 OKContent-Length: 1419Content-Type: multipart/related; boundary=example-4; type=application/alto-endpointcost+json--example-4Content-ID: <ecs@alto.example.com>Content-Type: application/alto-endpointcost+json{ "meta": { "vtags": { "resource-id": "endpoint-cost-pv.ecs", "tag": "84a4f9c14f9341f0983e3e5f43a371c8" }, "multi-cost-types": [ { "cost-mode": "array", "cost-metric": "ane-path" }, { "cost-mode": "numerical", "cost-metric": "routingcost" } ] }, "endpoint-cost-map": { "ipv4:192.0.2.34": { "ipv4:192.0.2.2": [[ "NET3", "AGGR1" ], 3], "ipv4:192.0.2.50": [[ "NET3", "AGGR2" ], 2] }, "ipv6:2001:db8::3:1": { "ipv6:2001:db8::4:1": [[ "NET3", "AGGR2" ], 2] } }}--example-4Content-ID: <propmap@alto.example.com>Content-Type: application/alto-propmap+json{ "meta": { "dependent-vtags": [ { "resource-id": "endpoint-cost-pv.ecs", "tag": "84a4f9c14f9341f0983e3e5f43a371c8" }, { "resource-id": "ane-props", "tag": "be157afa031443a187b60bb80a86b233" } ] }, "property-map": { ".ane:AGGR1": { "max-reservable-bandwidth": 10000000000, "persistent-entity-id": "ane-props.ane:MEC1" }, ".ane:AGGR2": { "max-reservable-bandwidth": 15000000000, "persistent-entity-id": "ane-props.ane:MEC2" }, ".ane:NET3": { "max-reservable-bandwidth": 50000000000 } }}--example-4¶The multipart filtered cost map resource and the multipart Endpoint CostService resource have no backward-compatibility issues with legacy ALTO clients andservers. Although these two types of resources reuse the media types defined inthe base ALTO Protocol for the "Accept" input parameters, they have differentmedia types for responses. If the ALTO server provides these two types ofresources but the ALTO client does not support them, the ALTO client willignore the resources without incurring any incompatibility problems.¶
The extension defined in this document is compatible with the multi-costextension[RFC8189]. Such a resource has a media type of either"multipart/related; type=application/alto-costmap+json" or "multipart/related;type=application/alto-endpointcost+json". Its "cost-constraints" field must beeither "false" or not present, and the Path Vector cost type must be presentin the "cost-type-names" capability field but must not be present in the"testable-cost-type-names" field, as specified in Sections 7.2.4 and7.3.4.¶
This extension is compatible with the incremental update extension[RFC8895].ALTO clients and serversMUST follow the specifications given in Sections 5.2 and6.7.3 of[RFC8895] to support incremental updates for a Path Vectorresource.¶
The extension specified in this document is compatible with the Cost Calendarextension[RFC8896]. When used together with the Cost Calendar extension, thecost value between a source and a destination is an array of Path Vectors, wherethe k-th Path Vector refers to the abstract network paths traversed in the k-thtime interval by traffic from the source to the destination.¶
When used with time-varying properties, e.g., maximum reservable bandwidth, aproperty of a single ANE may also have different values in different timeintervals. In this case, if such an ANE has different property values in twotime intervals, itMUST be treated as two different ANEs, i.e., with differententity identifiers. However, if it has the same property values in two timeintervals, itMAY use the same identifier.¶
This rule allows the Path Vector extension to represent both changes of ANEs andchanges of the ANEs' properties in a uniform way. The Path Vector part iscalendared in a compatible way, and the property map part is not affected by theCost Calendar extension.¶
The two extensions combined together can provide the historical networkcorrelation information for a set of source and destination pairs. A networkbroker or client may use this information to derive other resource requirementssuch as Time-Block-Maximum Bandwidth, Bandwidth-Sliding-Window, andTime-Bandwidth-Product (TBP) (see[SENSE] for details).¶
The constraint test is a simple approach for querying the data. It allows users tofilter query results by specifying some boolean tests. This approach isalready used in the ALTO Protocol. ALTO clients are permitted to specify either the "constraints" test[RFC7285][RFC8189] or the "or-constraints" test[RFC8189] to betterfilter the results.¶
However, the current syntax can only be used to test scalar cost types andcannot easily express constraints on complex cost types, e.g., the Path Vectorcost type defined in this document.¶
In practice, developing a bespoke language for general-purpose boolean tests canbe a complex undertaking, and it is conceivable that such implementations already exist(the authors have not done an exhaustive search todetermine whether such implementations exist). One avenue for developing such alanguage may be to explore extending current query languages like XQuery[XQuery] or JSONiq[JSONiq] and integrating these with ALTO.¶
Filtering the Path Vector results or developing a more sophisticated filteringmechanism is beyond the scope of this document.¶
Querying multiple ALTO information resources continuously is a generalrequirement. Enabling such a capability, however, must address generalissues like efficiency and consistency. The incremental update extension[RFC8895] supports submitting multiple queries in a single request and allowsflexible control over the queries. However, it does not cover the caseintroduced in this document where multiple resources are needed for a singlerequest.¶
The extension specified in this document gives an example of using a multipart message to encode theresponses from two specific ALTO information resources: a filtered cost map oran Endpoint Cost Service, and a property map. By packing multiple resources in asingle response, the implication is that servers may proactively push relatedinformation resources to clients.¶
Thus, it is worth looking into extending the SSE mechanism asused in the incremental update extension[RFC8895]; or upgrading to HTTP/2[RFC9113] and HTTP/3[RFC9114], whichprovides the ability to multiplex queries and to allow servers to proactively sendrelated information resources.¶
Defining a general multi-resource query mechanism is out of scope for thisdocument.¶
This document is an extension of the base ALTO Protocol, so the securityconsiderations provided for the base ALTO Protocol[RFC7285] fully apply when thisextension is provided by an ALTO server.¶
The Path Vector extension requires additional scrutiny of three securityconsiderations discussed in the base protocol: confidentiality of ALTOinformation (Section 15.3 of [RFC7285]), potential undesirable guidance fromauthenticated ALTO information (Section 15.2 of [RFC7285]), and availabilityof ALTO services (Section 15.5 of [RFC7285]).¶
For confidentiality of ALTO information, a network operator should be aware thatthis extension may introduce a new risk: the Path Vector information, when usedtogether with sensitive ANE properties such as capacities of bottleneck links,may make network attacks easier. For example, as the Path Vector information mayreveal more fine-grained internal network structures than the base protocol, anattacker may identify the bottleneck link or links and start a distributeddenial-of-service (DDoS) attack involving minimal flows, triggeringin-network congestion. Given the potential risk of leaking sensitiveinformation, the Path Vector extension is mainly applicable in scenarios where1) the ANE structures and ANE properties do not impose security risks on theALTO service provider (e.g., they do not carry sensitive information) or 2) the ALTOserver and client have established a reliable trust relationship (e.g.,they operate in the same administrative domain or are managed by business partners withlegal contracts).¶
Three risk types are identified inSection 15.3.1 of [RFC7285]:¶
To mitigate these risks, an ALTO serverMUST follow the guidelines inSection 15.3.2 of [RFC7285]. Furthermore, an ALTO serverMUST follow thefollowing additional protections strategies for risk types (1) and (3).¶
For risk type (1), an ALTO serverMUST use the authentication methods specifiedinSection 15.3.2 of [RFC7285] to authenticate the identity of an ALTO clientand apply access control techniques to restrict the retrieval of sensitive Path Vector information by unprivileged ALTO clients. For settings where the ALTO serverand client are not in the same trust domain, the ALTO server should reachagreements with the ALTO client regarding protection of confidentiality beforegranting access to Path Vector services with sensitive information. Suchagreements may include legal contracts or Digital Rights Management (DRM)techniques. Otherwise, the ALTO serverMUST NOT offer Path Vector services thatcarry sensitive information to the clients, unless the potential risks arefully assessed and mitigated.¶
For risk type (3), an ALTO service provider must be aware that persistent ANEsmay be used as "landmarks" in collaborative inferences. Thus, they should onlybe used when exposing public service access points (e.g., API gateways, CDN Interconnections)and/or when the granularity is coarse grained (e.g., when an ANE represents anAS, a data center, or a WAN).Otherwise, an ALTO serverMUST use dynamic mappings from ephemeral ANE names tounderlying physical entities. Specifically, for the same physical entity, anALTO serverSHOULD assign a different ephemeral ANE name when the entity appearsin the responses to different clients or even for different requests from thesame client. ARECOMMENDED assignment strategy is to generate ANE names fromrandom numbers.¶
Further, to protect the network topology from graph reconstruction (e.g.,through isomorphic graph identification[BONDY]), the ALTO serverSHOULDconsider protection mechanisms to reduce information exposure or obfuscate thereal information. When doing so, the ALTO server must be aware that informationreduction/obfuscation may lead to a potential risk of undesirable guidance fromauthenticated ALTO information (Section 15.2 of [RFC7285]).¶
Thus, implementations of ALTO servers involving reduction or obfuscation of thePath Vector informationSHOULD consider reduction/obfuscation mechanisms thatcan preserve the integrity of ALTO information -- for example, by using minimalfeasible region compression algorithms[NOVA] or obfuscation protocols[RESA][MERCATOR]. However, these obfuscation methods are experimental, and theirpractical applicability to the generic capabilityprovided by this extension has not been fully assessed. The ALTO serverMUST carefullyverify that the deployment scenario satisfies the security assumptions of thesemethods before applying them to protect Path Vector services with sensitivenetwork information.¶
For availability of ALTO services, an ALTO server should be cognizant that using aPath Vector extension might introduce a new risk: frequent requests for PathVectors might consume intolerable amounts of server-side computation andstorage. This behavior can break the ALTO server. For example, if an ALTO serverimplementation dynamically computes the Path Vectors for each request, theservice that provides the Path Vectors may become an entry point for denial-of-serviceattacks on the availability of an ALTO server.¶
To mitigate this risk, an ALTO server may consider using such optimizations asprecomputation-and-projection mechanisms[MERCATOR] to reduce the overhead forprocessing each query. An ALTO server may also protect itself frommalicious clients by monitoring client behavior and stopping service toclients that exhibit suspicious behavior (e.g., sending requests at a high frequency).¶
The ALTO service providers must be aware that providing incremental updates of"max-reservable-bandwidth" may provide information about other consumers ofthe network. For example, a change in value may indicate that one or morereservations have been made or changed. To mitigate this risk, an ALTO servercan batch the updates and/or add a random delay before publishing the updates.¶
This document registers a new entry in the "ALTO Cost Metrics" registry, perSection 14.2 of [RFC7285]. The new entryis as shown below inTable 1.¶
| Identifier | Intended Semantics | Reference |
|---|---|---|
| ane-path | SeeSection 6.5.1 | RFC 9275 |
This document registers a new entry in the "ALTO Cost Modes" registry, perSection 5 of [RFC9274]. The new entryis as shown below inTable 2.¶
| Identifier | Description | Intended Semantics | Reference |
|---|---|---|---|
| array | Indicates that the cost value is a JSON array | SeeSection 6.5.2 | RFC 9275 |
This document registers a new entry in the "ALTO Entity Domain Types" registry, perSection 12.3 of [RFC9240]. The new entryis as shown below inTable 3.¶
| Identifier | Entity Identifier Encoding | Hierarchy and Inheritance | Media Type of Defining Resource | Mapping to ALTO Address Type |
|---|---|---|---|---|
| ane | SeeSection 6.2.2 | None | application/alto-propmap+json | false |
SeeSection 6.2.1.¶
SeeSection 6.2.2.¶
None¶
None¶
SeeSection 6.2.4.¶
This entity type does not map to an ALTO address type.¶
In some usage scenarios, ANE addresses carried in ALTO Protocol messages mayreveal information about an ALTO client or an ALTO service provider.If a naming schema is used to generate ANE names, eitherused privately or standardized by a future extension, how(or if) the naming schema relates to private informationand network proximity must be explained to ALTO implementersand service providers.¶
Two initial entries -- "max-reservable-bandwidth" and "persistent-entity-id" -- areregistered for the ALTO domain "ane" in the "ALTO Entity Property Types" registry,perSection 12.4 of [RFC9240]. The twonew entries are shown below inTable 4, and their details can befound in Sections 12.4.1 and12.4.2 of this document.¶
| Identifier | Intended Semantics | Media Type of Defining Resource |
|---|---|---|
| max-reservable-bandwidth | SeeSection 6.4.1 | application/alto-propmap+json |
| persistent-entity-id | SeeSection 6.4.2 | application/alto-propmap+json |
"max-reservable-bandwidth"¶
SeeSection 6.4.1.¶
application/alto-propmap+json¶
To make better choices regarding bandwidth reservation, this property is essential for applications such as large-scale datatransfers or an overlay network interconnection. It may reveal the bandwidth usage of the underlyingnetwork and can potentially be leveraged to reduce the cost of conductingdenial-of-service attacks. Thus, the ALTO serverMUST consider such protectionmechanisms as providing the information to authorized clients only and applyinginformation reduction and obfuscation as discussed inSection 11.¶
"persistent-entity-id"¶
SeeSection 6.4.2.¶
application/alto-propmap+json¶
This property is useful when an ALTO server wants to selectively exposecertain service points whose detailed properties can be further queried byapplications. As mentioned inSection 12.3.2 of [RFC9240], the entity IDs may reveal sensitive information about theunderlying network. An ALTO server should follow the securityconsiderations provided inSection 11 of [RFC9240].¶
The authors would like to thankAndreas Voellmy,Erran Li,Haibin Song,Haizhou Du,Jiayuan Hu,Tianyuan Liu,Xiao Shi,Xin Wang, andYan Luo for fruitful discussions. The authors thankGreg Bernstein,Dawn Chen,Wendy Roome, andMichael Scharf for their contributions to earlier draft versions of this document.¶
The authors would also like to thankTim Chown,Luis Contreras,Roman Danyliw,Benjamin Kaduk,Erik Kline,Suresh Krishnan,Murray Kucherawy,Warren Kumari,Danny Lachos,Francesca Palombini,Éric Vyncke,Samuel Weiler, andQiao Xiang,whose feedback and suggestions were invaluable for improving the practicability andconciseness of this document; andMohamed Boucadair,Martin Duke,Vijay Gurbani,Jan Seedorf, andQin Wu, who provided great support and guidance.¶